[9] RFR (S): 8036117: MethodHandles.catchException doesn't handle VarargsCollector right (8034120 failed)

[Vladimir Ivanov]

http://cr.openjdk.java.net/~vlivanov/8036117/webrev.00/
https://bugs.openjdk.java.net/browse/JDK-8036117
84 lines changed: 74 ins; 3 del; 7 mod

I have to revert a cleanup I did for 8027827. 
MethodHandle.invokeWithArguments (and generic invocation) has unpleasant 
peculiarity in behavior when used with VarargsCollector. So, 
unfortunately, invokeWithArguments is not an option there.

Looking at the API (excerpts from javadoc [1] [2]), the following 
condition doesn't hold in that case:
   "trailing parameter type of the caller is a reference type identical 
to or assignable to the trailing parameter type of the adapter".

Example:
   target.invokeWithArguments((Object[])args)
   =>
   target.invoke((Object)o1,(Object)o2,(Object)o3)
   =/>
   target.invokeExact((Object)o1, (Object)o2, (Object[])o3)

because Object !<: Object[].

The fix is to skip unnecessary conversion when invoking a method handle 
and just do a pairwise type conversion.

Testing: failing test case, nashorn w/ experimental features (octane)

Thanks!

Best regards,
Vladimir Ivanov

[1] MethodHandle.invokeWithArguments
"Performs a variable arity invocation, ..., as if via an inexact invoke 
from a call site which mentions only the type Object, and whose arity is 
the length of the argument array."

[2] MethodHandle.asVarargsCollector
"When called with plain, inexact invoke, if the caller type is the same 
as the adapter, the adapter invokes the target as with invokeExact. 
(This is the normal behavior for invoke when types match.)

Otherwise, if the caller and adapter arity are the same, and the 
trailing parameter type of the caller is a reference type identical to 
or assignable to the trailing parameter type of the adapter, the 
arguments and return values are converted pairwise, as if by asType on a 
fixed arity method handle.

Otherwise, the arities differ, or the adapter's trailing parameter type 
is not assignable from the corresponding caller type. In this case, the 
adapter replaces all trailing arguments from the original trailing 
argument position onward, by a new array of type arrayType, whose 
elements comprise (in order) the replaced arguments."